1. Field of the Invention
The present invention relates to an endoscope, and more particularly relates to an endoscope which has an image pick-up device a plate like image sensor disposed within a viewing head thereof.
2. Description of the Prior Art
In addition to endoscopes having an optical fiber bundle as its image guide means, TV endoscopes have been proposed which have an image sensor as an image pick-up device such as a charge coupled device (CCD) which comprises a great number of small photosensitive elements (pixels) arranged in matrix. Such TV endoscopes which are far better than endoscopes heretofore used from the standpoint of durability, the effect of video signal managment and production costs, are in the improvement stage for practical application.
Now, an image sensor such as, for example, a CCD (charge coupled device) used as the forward end imaging device of the TV endoscope is comprised of a semiconductor and the intrinsic characteristics thereof tend to make it difficult to function under high temperature. More specifically, in view of the temperature characteristics of the CCD, dark current is increased in value under the igh temperature of about 40.degree. C., whereby the noises due to this dark current are increased to a considerable extent, so that the S/N (Signal/Noise) ratio is decreased.
Consequently, heat accumulation at a forward end portion of an insertable flexible section of the endoscope from the body temperature when a cavity of a living body is observed and heat generation by the image sensor itself exert adverse influences on the image pick-up. Because of this, there have been various proposals made including providing a special cooling device in the forward end portion of the endoscope. However, the provision of the special cooling device presents the disadvantages of complicating the construction of the forward end portion of the endoscope and increasing the size of the forward end.